1. Field of the Invention
The present invention relates to an interface control device.
2. Description of the Related Art
A removable data-storage medium such as a memory card is conventionally connected to an information processing device that is used as a host device. The information processing device may be a digital camera, a cellular phone, a personal computer (PC), and a Personal Digital Assistant (PDA). Data is transmitted/received between the host device and the memory card through an interface such as a universal serial bus (USB).
JP-A 2006-216011 (KOKAI) discloses a technique to transmit the data stored in the memory card to an other device other than the host device (hereinafter, “external read device”). Specifically, the memory card has a communication controller to communicate using radio medium. The communication controller is configured to be controlled by the external read device. The external read device can receive the data stored in the memory card without operating the host device. In addition, this reference describes that the memory card independently handles accesses from the host device and from the external read device.
JP-A 2008-147871 (KOKAI) discloses a communication system in which the external read device (for example, radio-communication device) directly controls the memory card connected to the host device. A relaying device having a radio interface exists between the memory card and the host device. The external read device transmits a request information to the relaying device. The request information includes an instruction to control the memory card. The relaying device controls the memory card according to the instruction.
In the above references, when the external read device tries to access to the memory card, the external read device first transmits/receives a data to/from the memory card using a transmission rate. Next, the memory card writes/reads the data to/from a memory (for example, flash memory) in the memory card using an access rate.
The access rate depends on a frequency of a clock signal (hereinafter, “clock frequency”) which is supplied by the host device. When the clock frequency is low, the access rate is also low regardless of the transmission rate. Since the low access rate becomes a bottleneck, the external read device can not access to the memory card using the high transmission rate. On the other hand, when the clock frequency is high, the access rate is also high regardless of the transmission rate. Especially, when the transmission rate is low, the high access rate may be wasted. In this case, a power consumption of the radio interface may become larger.
Moreover, the external read device may require address information of the memory card in order to access to the memory card. In JP-A 2006-216011 (KOKAI), the external read device may obtain the address information by adding a special function for getting the address information to an interface of the external read device. However, it is difficult for some information processing devices such as a PC using an existing interface to obtain the address information.